Bad cat or loose heat shield?
 

I just bought a 91 accord, it had a bad exhaust leak when I bought it so I had it repaired, ended up being the flex pipe, which is what I assumed, now that its quiet I have noticed that when I start the car, rev it up, it has an exhaust rattle, It only rattles when I am sitting in neutral revving the engine, or when I'm taking off. If I'm shifting gears at 25MPH plus it is not as noticeable.

Does the heat shield seem to be most suspect?

What are the symptoms of a bad cat?

Loose heatshield or bad cat might sound about the same. You need to get underneath & check. By hitting the heatshields with your knuckles or something like that (don't beat it too hard with a hammer); you can see whether it's the heatshields. Process of elimination can lead you to a broken catalyst.

When you're under there you'll notice there's several heatshields, many of them bolted to the floorpan above the exhaust pipe. Any of them can be loose.

Thanks for the help, I will crawl under there in a little while and see what I can find.

Don't oveloook the Exhaust A pipe from the manifold
 

I have been chasing a similar "rattle" at approx 2200 rpm for a year. Turned out to be the first pipe coming off the exhaust manifold. Mine lasted 23 yrs (93 Accord SE Coupe) so I can't complain but it nearly impossible to find a decent aftermarket replacement A pipe. Trying my third one this week from Walker. The issue is that there is an internal pipe and external pipe. I have heard it called an "air-gap" pipe to help with sound deadening and heat build up. Outside pipe is in good shape but the inside pipe has rusted and is rattling under load. Good luck !!!